1. Field of the Invention
This invention relates to a composition of soda-lime-silica glass suitable for the production of panes that may be used in the architectural field or the automobile industry. The composition according to the invention is especially adapted for production in the form of a continuous glass ribbon by the float glass technique.
2. Discussion of the Background
Compositions of soda-lime-silica glass used in this technique have been characterized by very slight variations from an average glass. The following composition, expressed in percentages by weight, is very representative:
______________________________________ SiO.sub.2 73.08 Al.sub.2 O.sub.3 0.11 CaO 8.94 MgO 3.88 Na.sub.2 O 13.68 K.sub.2 O 0.02 Fe.sub.2 O.sub.3 0.12 SO.sub.3 0.23 ______________________________________
This glass, which is notably characterized by a low content of iron oxides, enables glass sheets to be produced with a particularly high total light transmission factor under illuminant A (TL.sub.A). This characteristic is desirable for panes intended to be mounted on automobile vehicles or to be installed in buildings.
Iron, traditionally expressed as Fe.sub.2 O.sub.3, is distributed through the glass in the form of ferric oxide and ferrous oxide, the respective concentrations of which depend upon the degree of oxidation/reduction of the glass. The presence of ferric oxide enables the absorption of ultraviolet radiation and those radiations that have short wavelengths in the visible range of the spectrum. The presence of ferrous oxide makes possible the absorption of the radiations in the near infrared and those corresponding to the long wavelengths of the visible range. The latter phenomenon of absorption has the effect of reducing the total energy transmission factor (T.sub.g). These iron oxides, in particular FeO, contribute to the coloration of the glass.
A pane made from a glass of the type mentioned above has, for a large thickness, a non-negligible coloration in spite of the low content of iron oxides.